THE EFFECT OF RESIDUAL-STRESSES ON THE DEBONDING OF COATINGS .1. A MODEL FOR DELAMINATION AT A BIMATERIAL INTERFACE

An analysis is presented of how a general set of residual stresses is predicted to influence the debonding behaviour of a coating. This is oriented towards relatively thick coatings, in which significant through-thickness variations of residual stresses may occur. A through-thickness deposit crack is assumed to exist and the external loading is pure bending. An expression for the interfacial strain energy release rate, G(i), comprised of three terms, due to the applied loading, to the residual stresses and to an interaction term dependent on both, is derived. An experimental procedure to characterise the residual stress distribution is described. During interfacial fracture, the crack path, and therefore the loading state at the crack tip, are pre-determined by the plane of weakness. Since the critical value of G(i) for interfacial failure has been observed to be a function of this loading state, a procedure is described for determining the phase angle characterising it for a given applied load and residual stress state. The results of these analyses are presented for various generalised residual stress states. In the second part of this pair of papers, the model is applied to experimental data for thermally sprayed coatings.